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1. Field of the Invention
The present invention broadly relates to the field of orthopedic surgery, and more particularly, to computer assisted orthopedic surgery that uses two or more X-ray images of a patient""s bone to generate a computer-based 3D (three dimensional) model of the patient""s bone and a computer-based surgical plan for the doctor.
2. Description of the Related Art
Bone distraction in orthopedic surgery might well be considered one of the earliest successful forms of tissue engineering. Bone distraction is a therapeutic process invented in Russia in about 1951 for treating fractures, lengthening limbs and correcting other skeletal defects such as angular deformities. In bone distraction, external fixators are used to correct bone deformities and to lengthen bones by the controlled application of xe2x80x98tension-stressxe2x80x99, resulting in natural, healthy tissue.
FIG. 1 illustrates a prior art Ilizarov fixator 20 attached to a bone 22. The external Ilizarov fixator 20 is constituted of a pair of rings 24 separated by adjustable struts 28. The rings 24 are mounted onto the bone 22 from outside of the patient""s body through wires or half-pins 26 as illustrated in FIG. 1. The lengths of the struts 28 can be adjusted to control the relative positions and orientations of the rings 24. After the fixator 20 is mounted to the patient""s bone 22, the bone 22 is cut by osteotome (i.e., surgical cutting of a,bone) as part of the bone distraction process. Thereafter, the length of each individual strut 28 is adjusted according to a surgical plan. This length adjustment results in the changing of the relative position of the rings 24, which then forces the distracted (or xe2x80x9ccutxe2x80x9d) bone ends to comply and produce new bone in-between. This is termed the principle of xe2x80x9ctension-stressxe2x80x9d as applied to bone distraction.
The bone distraction rate is usually controlled at approximately 1 mm (millimeter) per day. The new bone grows with the applied distraction and consolidates after the distraction is terminated. Thereafter, the fixator 20 can be safely removed from the bone 22 and, after recanalization, the new or xe2x80x9cdistractedxe2x80x9d bone is almost indistinguishable from the old or pre-surgery bone. The bone 22 may be equipped with other units, such as hinges, to correct rotational deformities about one or a few fixed axes. Thus, controlled application of mechanical stress forces the regeneration of the bone and soft tissues to correct their own deformities. The whole process of deformity correction is known as xe2x80x9cbone distraction.xe2x80x9d
At present, the following nominal steps are performed during the bone distraction process: (1) Determine an appropriate frame size for the fixator (e.g., for the Ilizarov fixator 20); (2) Measure (e.g., from X-rays) the deformity of bone fragments (or the anticipated fragments after surgically cutting the bone) and obtain six parameters that localize one fragment relative to the other; (3) Determine (or anticipate) how the fixator frame should be mounted on the limb; (4) Input the parameters and measurements to a computer program that generates the strut lengths as a function of time required to correct the deformity; (5) Mount the fixator frame onto the bone fragments; and (6) Adjust the strut lengths on a daily basis according to the schedule generated in step (4).
The steps outlined in the preceding paragraph are currently executed with minimal computerized assistance. Typically, surgeons manually gather or determine the required data (e.g., fixator frame size, bone dimensions, fixator frame mounting location and orientation, etc.) and make their decisions based on hand-drawn two-dimensional sketches or using digitized drawings obtained by tracing X-ray images For example, a computerized deformity analysis (CDA) and pre-operative planning system (hereafter xe2x80x9cthe CDA systemxe2x80x9d) developed by Orthographics of Salt Lake City, Utah, USA, rates the boundary geometry of bones using X-ray images that are first digitized manually, i.e., by placing an X-ray image on a light table and then tracing the outline with a digitizing stylus, and then the digital data are fed into the CDA system. Thereafter, the CDA system assists the surgeon in measuring the degree of deformity and to make a surgical plan. The entire process, however, is based on two-dimensional drawings and there is no teaching of showing or utilizing three-dimensional bone deformity or bone geometry.
It is observed that in the complex area of bone distraction surgery, it is difficult, if not impossible, to make accurate surgical plans based solely on a limited number of two-dimensional renderings of bone geometry. This is because of the complex and inherently three-dimensional nature of bone deformities as well as of fixator geometry. Furthermore, two-dimensional depictions of surgical plans may not accurately portray the complexities involved in accessing the target positions of the osteotome and fixator pins surrounding the operated bone. Lack of three-dimensional modeling of these geometric complexities makes it difficult to accurately mount the fixator on the patient according to the pre-surgical plan.
After a surgeon collects the requisite data (e.g., fixator frame size to be used, patient""s bone dimensions, fixator frame mounting location and orientation, etc.), the surgeon may use the simulation software accompanying commercially available fixators (such as the Taylor Spatial Frame distributed by Smith and Nephew Inc. of 1450 Brooks Road, Memphis, Tenn., USA 38116) to generate a day-by-day plan that shows how the lengths of the fixator struts should be adjusted. Such a plan is generated after the initial and target frame positions and orientations are specified by the surgeon. However, the only functionality of the simulation software is a simple calculation of the interpolated frame configurations. The software does not provide any assistance to the surgeon about making surgical plans nor does it provide any visual feedback on how the fixator frame and bone fragments should be moved over time.
The Taylor Spatial Frame (shown, for example, in FIG. 16) with six degrees of freedom (DOF) is more versatile, flexible and complex than the Ilizarov fixator 20 in FIG. 1. Because of the sophistication of modern fixators (e.g., the Taylor Spatial Frame) and because of the limitations of the presently available bone distraction planning and execution systems, current computerized bone distraction procedures are error-prone, even when performed by the most experienced surgeons. As a result, the patients must typically revisit the surgeon several times after the initial operation in order for the surgeon to re-plan and refine the tension-stress schedule, or even to re-position the fixator. Such reiterations of surgical procedures are not only time-consuming, but incur additional costs and may lead to poorer therapeutic results while unnecessarily subjecting patients to added distress. It is therefore desirable to generate requisite bone and fixator models in three-dimensions prior to surgery so as to minimize the surgery planning and execution errors mentioned hereinbefore.
The discussion given hereinbelow describes some additional software packages that are available today to assist in the simulation and planning of bone distraction. However, it is noted at the outset that these software packages are not based on three-dimensional models. Further, these software packages are quite limited in their capabilities to assist the surgeon in making important clinical and procedural decisions, such as how to access the site of the osteotomy or how to optimally configure fixator pin configurations. Additional limitations of the present software systems include: (1) No realistic three-dimensional view of a bone and a fixator; (2) No usage of motion in surgical simulation; (3) Lack of an easy-to-use graphical user interface for user-friendliness; (4) No on-line database of standard or past similar cases and treatment data; and (5) No file input/output to store or retrieve previous case data.
In xe2x80x9cCorrection of General Deformity With The Taylor Spatial Frame Fixator(trademark)xe2x80x9d (1997), Charles J. Taylor refers to a software package from Smith and Nephew (Memphis, Tenn.) (hereafter xe2x80x9cthe Smith softwarexe2x80x9d) that utilizes the Taylor Spatial Frame for certain computations. However, the Smith software does not include any visual output to the user (i.e., the surgeon) and user needs to enter all data via a dialog box. Being mechanical in nature, the strut locations in a fixator are static. However, the Smith software does not account for whether a strut can be set to all the lengths necessary during the bone correction process. Further, the Smith software cannot calculate corrections that are due to malrotation (of the fixator) only.
As described hereinbefore, a software for computerized bone deformity analysis and pre-operative planning is developed by Orthographics of Salt Lake City, Utah, USA (hereafter xe2x80x9cthe Orthographics softwarexe2x80x9d). The Orthographics software creates the boundary geometry of bones using X-ray images that are first digitized manually as previously mentioned. Thereafter, the Orthographics software assists the surgeon in measuring the degree of bone deformity and to make a surgical plan. The entire process, however, is based on two-dimensional drawings and there is no support for showing or utilizing three-dimensional bone deformity or bone geometry. However, it is difficult to make accurate surgical plans based on a few such two-dimensional renderings considering the complex, three-dimensional nature of bone deformities and fixator geometry, and also considering he complexity involved in accessing the target positions of the osteotomy and fixator pins. This inherently three-dimensional nature of bone geometry and fixator assembly also makes it difficult to accurately mount the fixator on the patient""s bone according to the two-dimensional pre-surgical plan. For further reference, see D. Paley, H. F. Kovelman and J. E. Herzenberg, Ilizarov Technology, xe2x80x9cAdvances in Operative Orthopaedics,xe2x80x9d Volume 1, Mosby Year Book. Inc., 1993.
The software developed by Texas Scottish Rite Hospital for Children utilizes primitive digitization of the radiographs to generate three-dimensional representations of bones without any simulation. Additionally, the generated models are very primitive and do not show any kind of detail on the bone. For further reference, see Hong Lin, John G. Birch, Mikhail L. Samchukov and Richard B. Ashman, xe2x80x9cComputer Assisted Surgery Planning For Lower Extremity Deformity Correction By The Ilizarov Method,xe2x80x9d Texas Scottish Rite Hospital for Children.
The SERF (Simulation Environment of a Robotic Fixator) software has capability to represent a three-dimensional bone model. However, the graphical representations of the fixator frame and the bone by the SERF software are over-simplified. Furthermore, there is no mention of any user interface except for a dialog box that prompts a user (e.g., a surgeon) for a xe2x80x9cmaximum distance.xe2x80x9d Additional information may be obtained from M. Viceconti, A. Sudanese, A. Toni and A. Giunti, xe2x80x9cA software simulation of tibial fracture reduction with external fixator,xe2x80x9d Laboratory for Biomaterials Technology, Istituto Rizzoli, Bologna, Italy, and Orthopaedic Clinic, University of Bologna, Italy, 1993.
In xe2x80x9cComputer-assisted preoperative planning (CAPP) in ortiopaedic surgery,xe2x80x9d Orthopaedic Hospital, Medical College, University of Zagreb, Yugoslavia, 1990, Vilijam Zdravkovic and Ranko Bilic describe a CAPP and Computer Assisted Orthopedic Surgery system. The system receives feedback and derives a bone""s geometry from two two-dimensional scans. However, this system still uses the less sophisticated and less complex Ilizarov fixator 20 (FIG. 1) instead of the more advanced Taylor Spatial Frame.
In a computer-assisted surgery, the general goal is to allow the surgeon to accurately execute the pre-operative plan or schedule. One approach to fulfil this goal is to provide feedback to the surgeon on the relative positions and the orientations of bone fragments, fixator frame and osteotomy/coricotomy site as the surgical procedure progresses. These positions could be determined in real time by measuring, with the help of an infrared (R) tracking system, the positions of infrared light emitting diode (LED) markers strategically placed on the fixator frame, on cutting tools and on the patient. The relative positions of all these objects (and deviations from the planed positions) could then be displayed via a computerized image simulation to give guidance to the surgeon operating on the patient. Such a feedback approach is currently used to help register acetabular implants in artificial hip surgery using an Optotrak optical tracking camera from Northern Digital Inc. of Ontario, Canada. The Optotrak camera is capable of tracking the positions of special LEDs or targets attached to bones, surgical tools and other pieces of operating room equipment. However, for use in a computer-aided bone distraction system, the Optotrak camera and additional display hardware are too expensive to consider for a widespread bone distraction commercialization strategy.
It is estimated that, at present, less than 1% of orthopedic surgeons practice the bone distraction procedure and less than 5000 bone distraction cases are performed per year worldwide. Such relative lack of popularity may be attributed to the fact that learning the techniques for bone distraction is extremely demanding and time-consuming. Therefore, the average orthopedic surgeon does not perform these techniques. Thus, there is a significant number of patients for whom external fixation with distraction would be the treatment of choice, but because of the current complexity and cost limitations, these patients never benefit from advanced bone distraction procedures.
It is therefore desirable to develop a user-friendly (i.e., a surgeon-friendly) system that would make bone distraction a viable option for a much broader market of surgeons than are currently using this therapy. It is also desirable to devise a computer-based surgical planning service that simplifies frame fixation, decreases preoperative planning time and reduces the chances of complications, thereby making far fixation a relatively physician-friendly technique. To facilitate acceptance of complex bone distraction procedures to a wider segment of orthopedic surgeons, it is further desirable to overcome two primary limitations present in current surgical planning and execution software: (1) the lack of three-dimensional visual aids and user-friendly simulation tools, and (2) the lack of an accurate and economical registration (i.e., fixator mounting) scheme.
The present invention contemplates a method of generating a computer-based 3D (three dimensional) model for a patient""s anatomical part comprising defining a 3D template model for the patient""s anatomical part; receiving a plurality of 2D (two dimensional) x-ray images of the patient""s anatomical part; extracting 2D fiducial geometry of the patient""s anatomical part from each of said plurality of 2D x-ray images; and deforming the 3D template model using the 2D fiducial geometry of the patient""s anatomical part so as to minimize an error between contours of the patient""s anatomical part and those of the deformed 3D template model.
A computer assisted orthopedic surgery planner software according to the present invention may identify the 2D fiducial geometry of a patient""s bone (or other anatomical part under consideration) on the 3D template bone model prior to deforming the 3D template bone model to substantially conform to the contours of the actual patient""s bone. In one embodiment, after detecting the bone contour, the computer assisted orthopedic surgery planner software creates a 3D lattice in which the 3D template bone model is embedded. Thereafter, a free-form deformation process is applied to the 3D lattice to match with the contour of the patient""s bone, deforming the 3D template bone model in the process. Sequential quadratic programing (SQP) techniques may be used to minimize error between 2D X-ray images data and the deformed template bone data.
In an alternative embodiment, a template polygonal mesh representing a standard parametric geometry and topology of a bone is defined. The template polygonal mesh is then converted into a deformable model consisting of a system of stretched springs and bent springs. Then, multiple X-ray images of the patient""s bone are used to generate force constraints that deform and resize the deformable model until the projections of the deformed bone model conform to the input X-ray images. To further assist the bone geometry reconstruction problem, a standard library of image processing routines may be used to filter, threshold and perform edge detection to extract two-dimensional bone boundaries from the X-ray images.
In another embodiment, the present invention contemplates a computer-based method of generating a surgical plan comprising reading digital data associated with a 3D (three-dimensional) model of a patient""s bone, wherein the digital data resides in a memory in a computer; and generating a surgical plan for the patient""s bone based on an analysis of the digital data associated with the 3D model. A surgical planner/simulator module in the computer assisted orthopedic surgery planner software makes a detailed surgical plan using realistic 3D computer graphics and animation. The simulated surgical plan may be viewed on a display seen of a personal computer. The planner module may also generate a pre-surgery report documenting various aspects of the bone surgery including animation of the bone distraction process, type and size of fixator frame and its struts, a plan for mounting the fixator frame on the patient""s bone, the location of the osteotomy/coricotomy site and the day-by-day length adjustment schedule for each fixator strut.
In a still further embodiment, the present invention contemplates an arrangement wherein a computer assisted orthopedic surgery planner computer terminal is connected to a remote operation site via a communication network, e.g., the Internet. The computer assisted orthopedic surgery planner software may be executed on the computer assisted orthopedic surgery planner computer. A fee-based bone distraction planning (BDP) service may be offered via a network (e.g., the Internet) using the computer assisted orthopedic surgery planner software at the service provider""s site. An expert surgeon at the service provider""s site may receive a patient""s X-ray data and other additional information from a remotely-located surgeon who will be actually operating on the patient. The remotely-located surgeon may be a subscriber to the network-based BDP service. The expert surgeon may analyze the X-ray data and other patient-specific medical data supplied by the remotely-located surgeon with the help of the computer assisted orthopedic surgery planner software executed on the computer assisted orthopedic surgery planner computer. Thereafter, the expert surgeon may send to the remotely-located surgeon over the Internet the 3D bone model of the patient""s bone, a simulated surgery plan as well as a complete bone distraction schedule generated with the help of the computer assisted orthopedic surgery planer software of the present invention.
The computer assisted orthopedic surgery planner software of the present invention makes accurate surgical plans based solely on a number of two-dimensional renderings of the patient""s bone geometry. The software takes into account the complex and inherently three-dimensional nature of bone deformities as well as of fixator geometry. Furthermore, three-dimensional simulation of the suggested surgical plan realistically portrays the complexities involved in accessing the target positions of the osteotome and fixator pins surrounding the operated bone, allowing the surgeon to accurately mount the fixator on the patient according to the pre-surgical plan.
With the computer-aided pre-operative planning and frame application and adjustment methods of the present invention, the duration of fixation (of a fixator frame) may be reduced by an average of four to six weeks. Additionally, by lowering the frequency of prolonged fixations, substantial cost savings per patient may be achieved. Shortening of the treatment time and reduction of complications may lead to better surgical results and higher patient satisfaction. The use of the computer assisted orthopedic surgery planner software of the present invention (e.g., in an Internet-based bone distraction surgery planning service) may make the frame fixation and bone distraction processes physician-friendly by simplifying fixation, decreasing preoperative planning time, and reducing the chances of complications through realistic 3D simulations and bone models. Thus more surgeons may practice bone distraction, resulting in benefits to more patients in need of bone distraction.